This invention relates to coating compositions for architectural use, specifically adapted for applications to concrete or mortar surfaces, and more particularly to coating material containing a quaternary ammonium silicate as the principal component and having good adhesion to the substrate even at low temperatures.
In the prior art, quaternary ammonium silicates themselves have been used as a wetting agent or a coating material, and it is known that the films formed by drying a solution containing such quaternary ammonium silicate are insoluble in hot as well as cold water, and have excellent resistance to heat and fire. However, when a coating composition is prepared by adding the quaternary ammonium silicate as a binder and the composition, thus prepared, is applied to the substrate, exterior or interior, consisting of concrete or mortar, the resulting solid coatings are critically defective in water-resistance, strength and other properties.
The present invention is based on the discovery, resulting from extensive studies on the above-described drawbacks, that the use of a binder consisting of a quaternary ammonium silicate and a certain amount of an epoxide resin brings about a coating which has excellent adhesion when immersed in water, and also that further addition of a silica sol as the binder contributes to strength, which is obtained very quickly for the coating, even at lower temperatures.
In explanation, the above studies were directed to, the structure which was produced on the surface of the silica that was formed by the quaternary ammonium silicate, its capability of forming hydrogen bonds and its association ability as well as to the adsorbability of silanol groups contained in the silica. The study was also directed to the structure of the network of the siloxane bonding which was produced between the surface and inner layers of the coating formed through gelling when a silica sol was added as the binder. It was found that the network structure had remarked differences when the coating was as thick as 2 mm or more. It was then concluded that coatings having sufficient toughness or strength could not be obtained by mere mechanical bonding force, but only by the formation of a complex with a highly reactive and bonding epoxide resin.
The coating compositions of the present invention are distinguished by their capability of producing coatings having high resistance to repeated changes of temperatures and, accordingly, suitable particularly for application to houses and buildings, interior or exterior, in cold areas. The coatings thus produced can well stand severe climatic changes, involving repetition of freezing and thawing.